In the quest for substitutes for fossil fuels, attention frequently has turned to hydrogen as an alternate fuel. Its abundance in water insures a plentiful supply, and its combustion results in reformation of water in, at least ideally, a pollution-free process. However, major limitations in the exploitation of hydrogen-based energy production are storage and transportation difficulties. Storage as a gas requires the use of bulky, massive containers to contain hydrogen at high pressures. Storage as a liquid requires a substantial fraction of the energy available from hydrogen to be expended in the liquefaction process. Both modes of storage present hazard and safety problems, especially when hydrogen is envisioned as an energy source for motor vehicles.
Storage of hydrogen as a hydrided metal is a relatively recent development explored to obviate the problems enumerated above. This approach utilizes the property of certain metal alloys to dissolve hydrogen, that is, to incorporate hydrogen atoms into the metal lattice, and to form metal hydrides reversibly at moderate temperatures and pressures, thereby acting as a carrier or sponge for significant quantities of hydrogen to be used as a fuel. Such hydrided metal alloys are solids which are easily handled and which do not pose the safety problems associated with high pressure gaseous hydrogen or liquid hydrogen. The state of the art has been summarized by Reilly and Sandrock, Scientific American, February, 1980, pages 118-129.